It is known in the art to use metallic hose joints that can be fixed on hoses made of rubber or resin for connecting the hoses to different equipments. Hose joints of this type and particularly those for high pressure fluids should not leak during use at the portion where the joint and the hose are tightly connected. The hose joint must therefore have high and continuous sealing performance to prevent fluid leakage.
FIGS. 10 and 11 show examples of the prior art metallic hose joint.
The metallic hose joint 1 shown in FIG. 10 comprises a nipple 3 to be inserted into a rubber hose 2 and a sleeve 5 which is formed concentrically with said nipple 3, and is tightly engaged with the rubber hose 2 by means of annular caulking members 7, 7a that are formed by pressing the sleeve 5 in the radial direction.
The shown rubber hose 2 is provided with a reinforcement layer 13 between its inside rubber wall 9 and outside rubber wall 11 made of heat resistant rubber. The inside rubber wall 9 is made of soft rubber such as nitrile and neoprene rubber. The reinforcement layer 13 comprises braid, thread wound in spiral, or wire and the like. The outer periphery of the nipple 3 has circumferential serrations 15 to prevent slipping off of the hose.
The rubber hose 2 is inserted in the gap between the nipple 3 and the sleeve 5 of the above construction, and the caulking members 7 and 7a provided at two locations on the sleeve 5 are utilized to fixedly engage the rubber hose 2 with the joint 1 by a so-called two-stage caulking structure.
FIG. 11 shows another example of the a prior art hose joint which differs from the first example in the inner shape of the sleeve and in the caulking method.
The metallic hose joint la comprises a nipple 3a and a sleeve 5a. The nipple 3a is identical in shape with the nipple 3, but the sleeve 5a is provided on its inside face with an annular groove 17 extending in the circumferential direction. The sleeve is indented radially to form a so-called flat caulking member 7b.
To prevent fluid leakage via the faces where the nipple 3 or 3a and the sleeve 5 or 5a come in contact with the inner and outer walls of the prior art hose 2, tightening force exerted by the nipple 3, 3a and the sleeve 5, 5a may be increased. However, when the tightening force is increased too much, the inner wall 9 of the rubber hose may be broken by the serrations 15. Even if pressed, a portion of the rubber volume would shift to where the pressure is not acting, as the rubber is elastic and forms an annular bulge 19 or 19a along the entire circumference at the tip of the nipple 3, 3a (the end face in the direction of hose insertion). As the bulge 19 or 19a is subjected to substantial deformation, this portion would easily become deteriorated by repeated compressions, causing cracks over a short period of time.
Further, when the bulge 19 or 19a is formed, the tightening force would decrease for the volume of the rubber being shifted, failing to achieve the desired tightening.
As the temperature of the rubber hose rises when the equipment to which it is attached is in use, stress on the rubber between the nipple 3, 3a and the sleeve 5, 5a would increase due to thermal expansion. In other words, the stress of the rubber increases as the rubber temperature rises, and the sealing performance would temporarily improve. However, the rubber temperature drops with time after the operation of the equipment is suspended, causing gradual stress relaxation. As the time elapses, the stress relaxation accelerates. The rubber stress is thus decreased by being repeatedly subjected to temperature rise and drop, and the rubber hose would eventually lose its sealing property against the fluid.
The present invention has been created in view of the foregoing situation.
The first object of the present invention is to provide a metallic hose joint for hoses by improving the nipple to prevent its bulging and to thereby prevent stress relaxation.
The second object of the present invention is to provide a metallic hose joint for hoses which maintains high sealing performance over an extended use.